Metal pickling process



Patented Aug. 1, 1939 Y METAL HCKLING rnooEss David J. Beaver, Nitro, W. Va, assignor toMonsanto Chemical Company, St. Louis, Mm, a corporation of Delaware aD pplication September 14, 1937,

Serial No. 163,823"

15 Claims. (01. ma -sf, a (9-phenanthridyl) -benzoic acid; beta (9-phenan- I The present invention relates to the cleaning of metallic surfaces, and particularly to a new class of inhibitors, which are employed to prevent undue attack upon the surface of a metal when in contact with a pickling bath of an acid nature.

Pickling solutions for removing oxides from the surface of metals ordinarily consist very largely of a dilute solution of an inorganic acid such as sulfuric or hydrochloric acid. The acid although it dissolves the oxides and scale, also attacks the metal to some extent so that the acid is largely consumed and a certain amount of metal is lost. It also appears that the hydrogen liberated by the action of the acid on the metal has a serious embrittling efiect upon the metal being treated. The escaping hydrogen also carries with it a fine spray of the acid liquor from the picking bath which produces an atmosphere possessing corrosive properties and one which is injurious to health and damaging to equipment.

By the present invention, these objectionable features of the pickling process are substantially overcome or reduced to a minimum. More specifically, some of the objects of the present invention are to obviate over-pickling, embrittlement and pitting of the articles treated; to minimize the amount of metal lost in pickling; to increase the efficiency of the pickling operation; to prolong the efiective life of the pickling bath;

and particularly to facilitate the pickling operation. Other and further objects of the invention will be apparent from the followingdescription and accompanying examples.

To accomplish to as great an extent as possible the objects set forth in accordance with the present invention, there is added to the pickling bath an inhibitor or regulating agent which acts to restrain the action of the acid from attacking clean metal but assists scale, and other deposits or, in other words, the inhibitor causes the acid selectively to remove such materials without appreciably attacking the clean portions of the metal under treatment.

The new class of pickle regulators or inhibitors, comprise the phenanthridines, and particularly substituted phenanthridines as for example alkyl, or aromatic substituted phenanthridines. Said substituent preferably comprises a carboxylic group. The said carboxylic group may be further condensed with the phenanthridine nucleus to form a carbocyclic ring. By a phenanthridine is meant a compound containing a phenanthridine nucleus. Phenanthridine is a compound possessing the structure Examples of the new class of materials are in removing the rust,-

thridyl) -propionic acid; beta (Q-phenanthridyllacrylic acid; benzo semi-flavanthrene and the compound obtained by ring closure of beta (9-' phenanthridyl) acrylic acid.

The preparation of phenanthridines is described by Hollins, Synthesis of Nitrogen Ring Compounds; pages 383 to 387. However, the compounds which comprise the'preferred-class of materials are obtainable by heating'an ortho amino biphenyl with an acid anhydride to a. suitable temperature to form the imide and further heating in the presence of anhydrous zinc chloride according to the method of Koelsch, Journal American Chemical Society, vol. 58, page 1325 (1936). The compound so obtained may be further dehydrated with sulphuric acid to efi'ect ring closure in a manner analogous to that of obtaining anthraquinone from ortho benzoyl benzoic acid.

As specific embodiments of the invention the following substances were prepared and tested as pickling inhibitors:

Compound A. -Substantially equi-molecular proportionsof o-amino biphenyl and phthalic anhydride were heated to substantially 200 C. Thecrude product was purified by dissolving in acetone and precipitating by the addition of water to the acetone solution. To 110 parts by weight of the o-biphenyl phthalimide 'so formed 220 the mixture heated to substantially 270 C. with agitation. The crude product so formed was purified by dissolving in dilute aqueous caustic soda solution, filtering and precipitating 'with dilute hydrochloric acid, again filtering and drying the precipitate. The reactions involved fol- The product obtained as deflned'above was phenanthridine; naphtho phenanthridine; orthotested as hereinafter described.

PIC" 7 parts by weight of zinc chloride were added and" I C-OH II N The product, benzo-semiflavanthrene, was found on' testing to be a good pickling inhibitor.

Compound C.Succinic anhydride and o-amino biphenyl were reacted in a manner analogous to that described for Compound A. The product so obtained, which is believed to possess the formula of and which may be called beta (9-phenanthridyl) propionic acid was found on testing to be a good pickling inhibitor.

Compound D.Maleic anhydride and o-amino biphenyl were reacted in a manner analogous to that described for the preparation of Compound A. The product so obtained, which is believed to possess the structural formula of was found on testing to be a good pickling inhibitor.

In the examples set forth for carrying out the metal pickling process, conditions were imposed which duplicated, so far as possible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed. A portion of one of the preferredclass of compounds was incorporated in a pickling bath and its value as an inhibitor determined in the following manner: A test piece of 28 gauge hot rolled tin plate steel stock, approximately 4" x 3" in dimension, was immersed in the pickling bath, comprising substantially 750 c. c. of a water solution containing approximately 6% by weight of 66 B. sulfuric acid and a small portion of one of the inhibitors above described. The temperature of the bath was maintained at substantially '82 C. The steel test piece was thoroughly cleaned and weighed before immersion in the bath, and after 40 minutes pickling the test piece was again weighed, the difference in weight representing the metal loss during pickling. The metal loss per square inch of surface exposed compared with the metal loss per square inch of surface exposed of a similar test piece treated in an analogous manner but without the use of any inhibitor provides a measure of the inhibiting value of the compound employed. The results obtained upon testing the above described materials in this manner are summarized in the following table:

Table I Weight Weight loss Weight loss Inhibiting compound of inhibiof metal in grams per employed tor emduring square inch of ployed pickling surface exposed Compound A 0936 036 00150 Compound B 2340 .019 00079 Compound C. 0930 048 .00200 Compound D 0936 034 00140 0936 125 (D52) None 519 02163 It is apparent from the data set forth that the preferred class of materials constitutes. an important and highly eiiicacious group of inhibitors, as in all cases wherein one of the preferred inhibiting compounds was incorporated in the pickle liquor there resulted a great saving in the loss in weight of the steel test strips as compared with that resulting when no inhibitor was employed. Furthermore, as shown and which may be called beta- (9-phenanthridyl) acrylic acid, was found on testing to be an excellent pickling inhibitor.

Compound E.The product above, designated as Compound D, was dehydrated in a manner analogous to that described for preparing Comby the data, a greater saving in metal losses results from the use of a larger amount of the inhibitor than that employed in the majority of the examples. Moreover, the steel plates pickled in the presence of the inhibitors set forth are clean and not stained upon removal from the pickle bath.

Other modes of employing inhibitors of the class hereinbefore set forth in the acid pickling.

of metals are apparent to those "skilled in the art to which the invention pertains. The products described may also be employed in the presence of foaming agents, ionizable substances or other materials ordinarily used. Again, other acids than sulfuric acid may be employed in the pickle bath. Thus, hydrochloric acid as well as other inorganic acids may be employed in the pickle bath in conjunction with the preferred class of inhibitors in the manner hereinbefore set forth.

What is claimed is:

1. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of a compound containing a phenanthridine nucleus.

2. A process of pickling a metal which com-.

prises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of an aromatic substituted phenanthridine.

3. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a non-oxidizing mineral acid solution containing a small proportion of acid substituted phenanthridine.

4. A process of pickling a. metal which comprises subjecting the metal to be pickled to the action of a non-oxidizing mineral acid solution containing a small proportion of a product obtainable by ring closure of a carboxylic acid substituted phenanthridine. I

5. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of 0-(9-phenanthridyl) -benzoic acid.

6. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a-sulfuric acid solution containing a. small proportion of beta-(9-phenanthridyl) acrylic acid.

a carboxylic 7. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of benzo-semiflavanthrene.

8. A pickling bath for metal products which comprises a. mineral acid solution containing a .small proportion of a compound containing a phenanthridine nucleus.

9. A pickling bath for metal products which comprises a non-oxidizing mineral acid solution containing a small proportion of a carboxylic acid substituted phenanthridine.

13. A pickling bath for iron and steel products.

which comprises a. sulfuric acid solution containing a small proportion of benzo-semifiavanthrene.

14. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of a compound selected from the class consisting of a carboxylic acid substituted phenanthridine and products obtainable by a ring closure thereof.

15. A pickling bath for metal products which comprises a mineral acid solution containing a small proportion of a compound selected from the class consisting of a carboxylic acid substitued 40 phenanthridine and products obtainable by a ring closure thereof.

DAVID J. BEAVER. 

